1. Field of the Invention
The present invention relates to a pattern substrate structure converging the light emitting angles and a light emitting diode device using the same. More particularly, the present invention relates to a plurality of stripe-shaped parts on the substrate altering a light path and converging a light emitting angle to raise the light directivity and improve the illuminant efficiency of the light emitting diode device.
2. Description of Related Art
In recent years, the light emitting diode has been applied in various technical fields to get more and more popular in the art as well as essential for a human daily life. In addition, the light emitting diode has been gradually substituted for conventional illuminant apparatuses in the next generations. Therefore, developing a high-power, energy-efficient and high-performance light emitting diode has become the trend in the future. The nitride LED is one of the popular semiconductor materials because of its small size, no mercury pollution, high illuminant efficiency, long lifetime and other merits. Also, the illuminant wavelengths of the III-Nitride mostly cover the visible wavelengths so as to show a great potential for use in light emitting diodes.
The structure of a conventional III-Nitride light emitting diode includes a substrate and a n-type semiconductor layer, an active layer and a p-type semiconductor layer formed in sequence on the substrate. In order to increase the current diffusion and light extraction efficiency, there is a transparent conductive layer (ex. Indium Tin Oxide (ITO)) formed on the p-type semiconductor layer, and then a p-type electrode pad and a n-type electrode pad formed on the p-type semiconductor layer and the n-type semiconductor layer with ohmic contacts, respectively. With respect to an ideal light emitting diode, the illuminant efficiency will be 100% when the photons resulted from their recombination with the carriers in the active layer are radiated outward entirely. However, the photons can not be radiated outward entirely during the radiation due is to the optical loss; in such a case, the illuminant efficiency would be reduced.
Further speaking, the strain resulted from the lattice mismatch between the substrate and the epitaxial film of the above light emitting diode often leads to misfit dislocations, parts of which will extend to a crystal surface to form a threading dislocation. For example, an epitaxial Gallium Nitride (GaN) film on a sapphire substrate has a high defect density because of a lattice mismatch of 16% between the sapphire and the GaN film. Generally, there is always a dislocation density of 109˜1011 cm−2 to mitigate the crystal quality of the active layer and the quantum efficiency of the light emitting diode, so that the illumination will be decreased and the heat generated therefrom will raise the temperature of the light emitting diode to affect the illuminant efficiency.
In addition, the light of the active layer is radiated outward in multiple directions to provide a light emitting angle between 120 degrees and 140 degrees, which causes a lack of the directivity of the light emitting diode to further deteriorate the illumination, and the large light emitting angle will cause the light from the adjacent light emitting diodes to be interacted and even to be absorbed by the adjacent light emitting diodes after multi-chip package, such that the illuminant efficiency is reduced.